What killed the saber-toothed tiger, the mastodon and the mammoth, formidable animals that were on top of the food chain in North America 20,000 years ago? Was it fierce Stone Age hunters as has commonly been assumed, or the little-studied but very real phenomenon of abrupt climate change? This question is not just of academic interest, to be debated by pipe-smoking professors at conferences. The rapid natural climate changes at the end of the Ice Age could be mirrored by man-made global warming in the 21st century, leading to devastating consequences for the planet's biodiversity and the human race itself. As the Bush administration rebuffs international treaties and embarks on a leisurely and largely redundant 10-year study of global warming science, the evidence we have alreacy amassed points to a climatic emergency, and a vastly changed Earth in 2100 and beyond. To avert that possibility, scientists say we'd need to reduce emissions of the most important greenhouse gas, carbon dioxide (C02), from transportation and industry by 80 percent, a near impossibility given current political realities.
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